1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device with a touch panel and a method of fabricating the same. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for making a user comfortable in writing and providing a slim dimension of the liquid crystal display device.
2. Discussion of the Related Art
In general, a touch panel is mounted on a display device of a notebook computer, which serves as an input device for position information by a user without an additional keyboard or mouse. The touch panel has been used for a graphic process such as CAD. The touch panel is referred to as a touch screen, a digitizer, a tablet or an electric graphic input panel (EGIP).
Depending upon a sensing method when a user touches a display surface, touch panels are classified into a resistive type, a capacitive type, and an electromagnetic type. In the resistive type touch panel, a current change is detected according to the position of a touching point with applying a DC voltage. Meanwhile, in the capacitive type touch panel, the position of a touching point is detected by a capacitance coupling with applying an AC voltage. Also, in the electromagnetic type touch panel, the position of a touching point is detected by detecting a resonant frequency resonated as an induction voltage with applying an electromagnetic field.
The respective type touch panels have different signal-amplification, resolution, design and process technology characteristics, so that the type of the touch panel is selected by a purpose of a display device using the touch panel in considering economical efficiency and endurance as well as electro-optics, electrical, mechanical, environment-resisting, and input characteristics.
A resistive type touch panel according to the related art will be described with reference to the accompanying drawings. FIG. 1 is a cross-sectional view illustrating a resistive type touch panel according to the related art. As shown in FIG. 1, the resistive type touch panel according to the related art includes upper and lower substrates 1 and 2, transparent electrodes (not shown), and spacers 5. The transparent electrodes (not shown) having a predetermined resistance value are formed on opposing surfaces of the upper and lower substrates 1 and 2, and the spacers 5 are formed between the upper and lower substrates 1 and 2 for maintaining an interval therebetween. In this case, both upper and lower substrates 1 and 2 are formed of glass substrates, or the upper substrate 1 is formed of a polyethylene terephtalate (PET) layer, and the lower substrate 2 is formed of a glass substrate.
In the resistive type touch panel, when a portion of the upper substrate 1 is touched with a finger 3 or a pen 4 at a predetermined pressure, the transparent electrodes formed on the opposing surfaces of the upper and lower substrates are in contact with each other. As a result, a controller (not shown) reads a voltage value variable by a resistance value of a touching point, thereby detecting coordinates of the touching point.
Meanwhile, the electromagnetic type touch panel has lately attracted attention because it detects more accurate position of the touch point than the resistive type touch panel. The electromagnetic type touch panel includes a digitizer and a stylus pen. The digitizer includes two sets of array coils perpendicular to each other, and the stylus pen is used for hand-in of a predetermined position on the digitizer.
FIG. 2 is a cross-sectional view illustrating a related art electromagnetic type touch panel. As mentioned above, the related art electromagnetic type touch panel includes a digitizer and a stylus pen. Referring to FIG. 2, the digitizer includes a sensor board 6, a shield plate 8, an adhesive 9, and a digitizer board 11. The digitizer generates an electromagnetic field, applies the electromagnetic field to a stylus pen 7, and receives an electromagnetic wave resonated at a touching point of the stylus pen 7, thereby detecting the touching point of the stylus pen 7. The shield plate 8 is formed of a metal material below the sensor board 6 for excluding the electromagnetic wave generated from the sensor board 6. Also, the shield plate 8 is attached to the sensor board 6 by the adhesive 9, and the digitizer board 11 is connected to the sensor board 6 by a connector 10 for driving the sensor board 6. Although not shown, the sensor board 6 includes a plurality of X-axis and Y-axis coils having loop-shaped structures for generating an electromagnetic field by receiving a current from a power source. The digitizer board 11 includes a circuit (not shown) for driving the sensor board 6, and a plurality of ICs 11a. 
The stylus pen 7 for inputting position information on the sensor board 6 includes a coil 12 and a capacitor 13. The coil 12 generates a current by receiving the electromagnetic field from the sensor board 6, and then generates an electromagnetic wave by the receiving the current. Also, the capacitor 13 charges and discharged the current generated in the coil 12. Accordingly, the electromagnetic type touch panel detects the position of the stylus pen 7 by using the electromagnetic of the stylus pen 7 and the sensor board 6, so that the direct detection of the stylus pen 7 is obtained. As a result, a user can perform fine and elaborate work on the electromagnetic type touch panel by controlling the thickness and the strength of color.
The electromagnetic type touch panel will be explained in more detail as follows. FIG. 3 is a circuit diagram schematically illustrating the sensor board and the stylus pen in the related art electromagnetic type touch panel. Referring to FIG. 3, the sensor board 6 of the electromagnetic type touch panel sequentially inputs AC voltages 16 to the plurality of loop patterns 15 connected to one ground terminal 14, so that the electromagnetic field is generated in the loop patterns 15. In other words, the loop pattern 15 and the stylus pen 7 respectively generate a loop-shaped solenoid. Thus, in case the current flows to the loop pattern 15, the electromagnetic field is generated at the direction perpendicular to the loop pattern 15.
Also, the stylus pen 7 is resonated with the electromagnetic field, so that the stylus pen 7 holds the resonant frequency for a predetermined time period, and then discharges the resonant frequency. In other words, the resonant frequency is stored in the capacitor 13 of the stylus pen 7 instantaneously, and discharged. Then, the discharged current from the stylus pen 7 generates the electromagnetic field by the loop pattern 15, thereby generating the loop current in the loop pattern 15. Subsequently, the sensor board 6 receives the electromagnetic field output from the stylus pen 7, and then switches a terminal to which the AC power source 16 is applied. As a result, the electromagnetic wave received in the sensor board 6 is changed to a voltage value, and then a controller (not shown) reads the changed voltage value, thereby detecting the coordinates of the stylus pen.
FIG. 4 illustrates an electromagnetic wave between the sensor and the stylus pen in the related art electromagnetic type touch panel. Referring to FIG. 4, an electromagnetic induction between the loop pattern 15 and the stylus pen 7 in the sensor board 6 is repetitively performed in a short time, so that movement of the stylus pen 7 on the sensor board 6 can be detected. Arrows 18 of the drawing indicate the direction of the electromagnetic field. Also, a signal intensity of the stylus pen 7 detected through the loop pattern 15 will be described with reference to FIG. 5. A step-shaped signal 19 corresponds to each loop pattern (15 of FIG. 3), and the peak of the step-shaped signal 19 corresponds to the position of the stylus pen 7. As a result, the electromagnetic type touch panel detects the correct position of the stylus pen 7 by using the electromagnetic induction of the loop pattern 15 of the sensor board 6 and the stylus pen 7.
FIG. 6 is a cross-sectional view illustrating the related art LCD panel. As shown in FIG. 6, the related art LCD panel includes a lower substrate 27, an upper substrate 28, a liquid crystal layer 32, and a ball spacer 33. The lower substrate 27 includes a pixel electrode 25 to which a video signal voltage is applied by switching a thin film transistor T. The thin film transistor T includes a gate electrode 20, a gate insulating layer 21, a semiconductor layer 22, and source/drain electrodes 23a and 23b. Also, the upper substrate includes a black matrix layer 29 for blocking out light from portions except for the pixel electrode 25, a color filter layer 30 for displaying R/G/B color, and a common electrode 31. The liquid crystal layer 32 is formed between the upper and lower substrates, and the ball spacer 33 is formed to maintain a constant interval between the upper and lower substrates. First and second polarizing plates (not shown) are formed on the external surfaces of the upper and lower substrates 27 and 28 for polarizing the light, and a backlight is formed below the lower substrate 27 for irradiating the light to the LCD panel.
A schematic corss-sectional view of the related art electromagnetic type touch panel attached to the LCD device will be described with reference to FIG. 7. FIG. 7 illustrates an LCD device integrated with a related art electromagnetic type touch panel. As shown in FIG. 7, the LCD device 40 includes an LCD panel 43, first and second polarizing plates 43a and 43b, a backlight 44, and a case top 41. The first and second polarizing plates 43a and 43b are respectively formed on the external surfaces of the upper and lower substrates of the LCD panel 43, and the backlight 44 is formed below the LCD panel 43 for irradiating the light to the LCD panel. Also, the case top 41 is formed to connect the LCD panel 43 having the first and second polarizing plates 43a and 43b to the backlight 44.
Furthermore, the LCD device includes a sensor board 6, a shield plate 8, and a digitizer board 11. The sensor board 6, the shield plate 8, and the digitizer board 11 are sequentially positioned below the LCD device 40. The sensor board 6 generates an electromagnetic wave, and detects the position of a stylus pen by detecting the electromagnetic wave from the stylus pen 7. Also, the shield plate 8 is formed for excluding the electromagnetic wave generated from the sensor board 6. The digitizer board 11 is formed below the shield plate 8, and is connected to the sensor board 6 by a connector 10 for driving the sensor board 6. With this configuration, a driving circuit 45 is positioned below the shield plate 8 for driving the LCD panel 43.
Next, a passivation substrate 42 is formed in parallel with the LCD device 40 for protecting the LCD device 40, and attached to the top case 41 by an adhesive. Accordingly, when the stylus pen 7 is positioned on the upper surface of the passivation substrate 42, the position of the stylus pen 7 is detected by the electromagnetic field induction between the stylus pen 7 and the sensor board 6. In this case, the ball spacer (the reference numeral 33 of FIG. 6) is used for maintaining a cell gap between the upper and lower substrates of the LCD device 40. That is, in case of a direct contact between the stylus pen and the LCD device 40, the ball spacer 33 may be moved between the upper and lower substrates by a pressure, thereby generating ripples in the liquid crystal. As a result, the LCD device may be deteriorated. In this respect, it is required to maintain a predetermined distance d between the LCD device 40 and the passivation substrate 42. For this, a bezel 46 is formed in the circumference of the passivation substrate 42 for securing the passivation substrate 42 to the LCD device. The passivation substrate 42 is formed of a glass substrate.
However, the LCD device integrated with the electromagnetic type touch panel according to the related art has the following disadvantages.
In case of mounting the related art electromagnetic type touch panel to the LCD device by using the stylus pen, the stylus pen may slide on the surface of the passivation substrate since the passivation substrate is formed of a glass substrate, and the tip of the stylus pen is formed of a plastic material such as polyacetal, so that it is hard to make a user comfortable in writing. Also, it is required to maintain a uniform cell gap between the LCD device and the passivation substrate, so that the visual difference may cause picture images of the stylus pen and the LCD device. That is, the pointing position of the stylus pen may be different from the pointing position recognized by the user.
In case of mounting the related art electromagnetic type touch panel to the LCD device, a predetermined distance is maintained between the passivation substrate and the LCD device, and the passivation substrate is formed of a glass substrate, so that the total thickness and the weight of the LCD device are increased, thereby lowering a mobility.